There are two main ways that radiation can damage DNA inside living cells. Radiation can directly hit the DNA molecule, ionizing and damaging it. Alternatively, radiation can ionize water molecules, producing free radicals that react with and damage DNA molecules. Ionizing radiation is a type of high-energy radiation that is capable of releasing electrons from atoms and molecules that generate ions that can break covalent bonds.
Ionizing radiation directly affects the structure of DNA by inducing DNA breaks, particularly DSB. Side effects are the generation of reactive oxygen species (ROS) that oxidize proteins and lipids, and also induce various DNA damage, such as the generation of abasic sites and single-stranded breaks (SSB). Taken together, all of these changes induce cell death and mitotic insufficiency. Radiation and electrons bombarded by radiation move randomly inside the cell, damaging the various molecules that form it.
Chromosomal DNA inside the cell nucleus can also be damaged. Ionizing radiation, such as gamma rays, x-rays, and radioactive particles, can cause cancer by damaging DNA. However, it is not known how this occurs or how many tumors are caused by radiation damage.